#!usr/bin/node

const {Readable} = require("stream");

const rd = new Readable();

let c = 'a'.charCodeAt(0);

rd._read = () => {
  if(c > 'z'.charCodeAt(0)) {
    rd.push(null);
    return ;
  }
  rd.push(String.fromCharCode(c++));
}

rd.pipe(process.stdout);
